I'm a completely new developer in NodeBB and I have started developing a custom theme with Vanilla as base theme but I have two main doubts that are probably linked.

First of all, I would like to modify the default value of "Custom Class" attribute in theme configuration related with category view.

Admin > Manage > Category Settings:

0_1483372017464_Screen Shot 2017-01-02 at 16.40.55.png

But I think it's not theme related but global variable related.
Anyone can help me to find out where those values are coming from and how can I change the default behaviour?

The second one is also related. I would like to add a new custom field in the config screen:

0_1483372227886_Screen Shot 2017-01-02 at 16.40.45.png

Similar to the "Category Image" one, but with other name, in order to use it as category background image for instance...

I really appreciate your help!